Changing the resonant frequency

I have a turbo turning 10,454 rpm with 17 blades creating a blade pass frequency of 2961 Hz. It seems to be exciting the pipe connected to the output of the turbo. I measured the 115 bB sound at about 2800 Hz with an uncalibrated instrument. This is a large ET24 turbo on a 4000 hp engine, it is about 24" in diameter and mounted about 30 feet off the engine. Each one of these turbos end up with custom built piping and this one is very loud. I did not get a chance to find the resonant frequency of the pipe with a bump test because the engine couldn't be shut down.

But guessing that the pipe weighs around 80 to 100 pounds, could I lay a cheap 40lb bag of cement on it and have a significant change in the pipes resonant frequency? Ot does it need to be physically attached to have a good impact?