my dog is a shizu heis 14 yrs old why is his tummy thumping?

Answer 1

You are hearing his heartbeat through his stomach.

Answer 2

I have no idea.  I suspect a VETERINARIAN would know.  Try one.

Answer 3

How can we possibly know?  The thing I do know is that any caring owner would get a 14 year old dog to the vet with NO delay if there seems to be something wrong.