I have an estate Meerschaum pipe that does that. It sounds like somebody gargling mouth wash every time I take a draw on it. (once the pipe has heated up) I've thought of re-drilling the air hole to see if that makes any difference, but haven't gotten around to it yet.
The limiting factor on the older meers is usually the screw in tenon. They have a very small air hole. Just use a small drill bit and twist by hand to ream the hole, go very slow. Start small and go up a drill size if needed. I've done that to a few of my older meers and it makes a big difference. One of the meers though I had to use the drill bit with an electric drill- it was tough plastic.