sewer pump noise

[John Arnold]

New construction bathroom sewer pump sounds fine and quiet while operating, but after pump shuts down, it starts making a noise like an out-of-balance washing machine for about 15-20 seconds. The pipes shake while this is going on, too.
Anyone know what would cause this?

[wayne soper]

John, Thats the water washing back down the pipe and smashing on to the backflow preventer.
Wait till the hard stuff gets in there:D
They never support the pipes well and they shake like there's an earthquake.
I always write it up as requireing proper support.
We don't want those connections breaking loose.

[John Arnold]

Wayne - Thanks! I don't see many of these, and ones I have seen didn't make this noise.