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Not much useful info there. Not that you've failed to
clearly describe the symptoms, but not much to go
on for a solution. No way from that info to blame it
on either the bass or the amp.
One thing you did NOT say is "It's got a new battery"
so be sure you can say that. I don't know what the
piezos sound like on a weak battery, but the battery
does power the buffer circuit which allows the piezos
to be played thru a typical amp without clacking and
clicking. Piezos lacking any buffering will clack, click,
and sound "cruntchie" thru a typical amp [an atypical
amp would be an acoustic instrument amp with very
high input impedence].
Another thing not mentioned is whether you've had
any local tech look into it, or whether it's still under
warrantee.
P.S. Unless you own the only bass amp in a 100 mi
radius, it's easier for you to determine whether it's
your amp or your bass, than it would be for us to do
so via online discussion.
So ... fresh battery and some other amp, then you
will have more useful info for your next step [if you
still need a next step].