On a DK-24 system the MOH has become distorted, it sounds great into the PCTUS1A. And when you monitor it thru one of the speakerphones. But it's distorted to callers on hold. It worked it one time.
Is it my PCTUS or PCOU card?

I think your processor has a trim pot for MOH volume. Make sure that your MOH source isn't over-driving the processor. Try to adjust your source and the trim pot to achieve a happy balance. I know it sounds good when you monitor but try a different source just for S&Gs..

Are you checking it from a cell phone ?

I checked with both cell & landline, sounds like the audio is saturating something. And trimpot was adjusted. I'm thinking it must be the CO line card if MOH feeds in thru processor card and the 8 port station card is receiving clear music, thru the backplane. But it's distorted to caller's on hold.
any thoughts?

I'm saying the station card must be good if I can press 480/481 to toggle MOH thru a speakerphone and it sounds great there.

Try swapping for an RCOU card, the PCOUs are very old and the dial tone cards are VERY cheap and easy to swap. Its feeding through the PCTUS fine so it can't be that.

Has the customer changed network provider recently?

I swapped out the CO line card today and it sounds much better. I put my butt set on the CO, while on hold, to adjust the level. Sounds great calling from a landline, not too good from a cell phone.
Thanks for all the help.