My Big Hauler sound card makes a strange burp noise rather than a chuff noise.  It is an older version without the volume control knob.  Looking for ideas on what to check.  I have verified that the problem is in the tender and not the locomotive.  I had another one that did the same thing but it had a visibly damaged (leaking) capacitor.  Changing that fixed it.  Any thoughts will be greatly appreciated.

So what turned out to be the problem with this locomotive?