Frustrated with new pre-amp and need advice

Hello all. I just bought a new tube preamp from a well-respected company. I'd rather not say who at this point because I'm still trying to work with them. But I am not real satisfied with the responses I've gotten thus far and need to know if my concerns are valid.

There are two main problems: (1) whenever I change sources or go passed 0 volume, I get a loud thump through my speakers. (2) When I have the phono input selected and i'm listening to an lp (via the internal phono board) but my cd is spinning too, I can clearly hear the CD source. It's intruding into the phono input.

So the manuf. rep has pretty much blamed problem #1 on either my ground connection or my power amp. However, when I use another pre amp (a peachtree decco), this problem doesn't happen. So how can it be a problem with my ground or amp?

For problem #2, they've not commented on what could be going on, and their silence doesn't make me feel warm and fuzzy.

So I'd most like to know if others ever have similar problems with any of their gear, if they indicate a defect in the equipment, or are these issues things I'll have to learn to live with.

I appreciate all comments!

Steve