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Wait... what was that? Sounds of the city explained

Every once in awhile, residents hear or see something around town that just doesn't have any immediate explanation. This week, we tracked a few of them down and found out what they are.

Thursday night church bells?

During the summer months, anyone in the area of Eighth and Eddy streets around 7 p.m. or 8 p.m. on a Thursday probably would have heard church bells ringing.

The bells belong to St. John's Lutheran Church. Every summer, the church offers Thursday evening worship services as an additional alternative to traditional Sunday services. The Thursday services started at 7 p.m. and opened with the bells. About 45 minutes later, the bells ring again briefly. The second set is part of the Lord's Prayer, and the bell is rung while the congregation says the prayer.

Every service at St. John's — including regular Sunday morning worship, special services and Wednesday evening lenten worship — follows the same pattern, with bell rings at the beginning of the service and during the Lord's Prayer. The Thursday services have stopped for the year, so those won't be heard again until next summer.

What's whistling downtown?

One reader asked us about a whistle-type sound that could be heard in the downtown Hastings area. Unlike the church bells, this was an irregular occurrence, sounding during the day, evening and weekends with no apparent pattern.

Answer 1 — As it turns out, the sound comes from the railroad bridge on the east side of downtown. The bridge, operated by CP Rail, opens and closes for barge traffic moving up and down the river. Every time the bridge opens and every time it closes, a high-pitched bridge horn sounds for about one or two seconds.

According to CP Rail staff, the number of times per day the horn goes off varies from day to day, depending on barge traffic. It's programmed into the bridge mechanics, so the horn automatically sounds whenever the bridge is about to move. The sound is meant to be a warning for people who might be working on or near the bridge, and it can happen at any time of day or night, on weekdays and weekends.

Answer 2 — There's another answer for recent whistling noises. For a few days last week, crews working on the Highway 61 bridge's south approach were using a pneumatic powered grout pump. The pump mixes and pumps grout into the post-tension tendons of the bridge, and makes a whistling noise. Crews started this work early in the morning, at 2 a.m. or 4 a.m. and continued it into the afternoons. The grouting work was finished late last week.

According to the Post-Tensioning Institute, "Post-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons."

The tendons run through the concrete and are stretched in a way that pulls the concrete pieces tightly together. Post-tensioning increases the load bearing capacity of the concrete. The grout is pumped into the ducts that hold the tendons, protecting it from corrosion and binding it to the concrete inside the ducts.

What's popping in the Industrial Park?

Every so often, an extremely loud pop or bursting sound can be heard in the Hastings Industrial Park, along Spiral Boulevard.

It comes from Dowco Valve Company. The company specializes in pressure relief valve repairs and sales. In the repair process, valves are tested to make sure they will function properly under pressure. Valves are placed on a testing station inside the building and have air, steam or liquid pressurised in them. The valves are designed to stay closed until a certain pressure is reached, and then they're supposed to open. Testers increase the pressure to the intended breakpoint and a little beyond to make sure the valve opens. When it does, it produces the noise, which can be quite loud when testing larger valves.

Pressure relief valves are critical pieces to a variety of systems, including air compressors, piping systems, boilers, storage tanks and more. Their basic function is to keep systems from overloading and bursting from too much pressure.

Storm sirens the first Wednesday of the month?

It's a sunny day, not a cloud in the sky, perfect for outdoor recreation, and suddenly you hear the storm sirens sounding all around the city. What's going on?

The first Wednesday of each month at 1 p.m., the Dakota Communications Center (DCC) runs a test of its outdoor warning device, commonly known as the storm sirens. Sirens in Hastings, Apple Valley, Burnsville, Farmington, Inver Grove Heights, Dakota County, Eagan, Lakeville, Mendota Heights, Rosemount, South St. Paul and West St. Paul are all operated and tested by the DCC.

Monthly Wednesday tests aren't anything to be concerned about, but what if you hear a siren at another time? Sirens can be activated in case of a severe thunderstorm warning or tornado warnings, or at the request of law enforcement.

Sirens are intended to serve as warnings to people who are outdoors. Sirens sound before severe weather arrives so that people who are outside have an opportunity to get inside and seek information before the system hits. Once a storm arrives, it can cut out power to sirens as well as radios and televisions.

Why are all those planes flying over Hastings?

Some days, the sky over Hastings is teeming with aircraft. Others, there's not a plane in sight. We got an explanation from the Metropolitan Airports Commission (MAC) as to why this is:

The flow of air traffic depends on several factors, but a primary one is wind. Wind conditions are gauged on the airfield and at altitudes up to 3,000 feet. When airfield wind speeds reach about 7 to 10 miles per hour, air traffic control assigns the runways that provide pilots with the greatest degree of headwind. There will be occasions when the wind is calm or light and variable on the surface, but stronger aloft. When this happens, air traffic control designates the runways in use that accommodate arriving traffic. Some of the runways at the Minneapolis-St. Paul Airport will send aircraft right over the Hastings area.

Taking off and landing with a headwind (the plane is moving against the wind) increases the airspeed. For example, a plane moving down the runway at 80 knots against a 10 knot headwind experiences an airspeed of 90 knots. Aircraft need a certain airspeed to take off and land, and taking advantage of headwinds means they'll require a shorter distance on the runway.

More information about flight tracking and runway use at the airport is available at