Suddenly I hear my rear drums retracting for some reason

[redfishsc]

This is on a 1999 C 1500 sub. For some reason, I am noticing the sound of my rear drums retracting when I let off of the brakes. Makes something like a "whump" thump.

Maybe they made this noise all along and I've never noticed it, but it's really obvious now. I cannot "not hear it".

It is absolutely the brakes, because I can press the brakes again and then let off, and it makes the same thump. Easily repeatable.

It's definitely not the "thump" you sometimes get from the driveshaft settling in the trans.

Anyone else get this?

Brakes work like a champ, this old Sub has nice, stout brakes. Drums and shoes new rebuilt last year including brake cylinders

 

[RichLo]

sounds like an axle seal may have leaked some oil onto one of your rear brake shoes, or a broken spring. have you taken the drums off yet to check for anything abnormal?

 

[redfishsc]

Not yet, I've actually had my head buried in a head gasket replacement on a different truck. How would the oil from the rear end cause that noise? Just curious, I would not have guessed this as a potential problem.