Never, seriously I would make a total fool of myself. Besides (I've tried it once on a private tennis court on vacation) it only serves to make my strokes more uncontrollable so it doesn't work for me.
I usually hit with guys so I feel the need to put a bit extra on my shots so sometimes I make noise. But nothing obnoxious like the country club women who come and hit on Saturday mornings
I do grunt when I'm running forward to catch a ball only, just like Sara In other circumstances - very rarely. Oh ... and sometimes when I feel that I am going to make an error I scream ''o nie...'' ''oh no!'' or ''ai'' or something close to it
A regular opponent told me last week that I always grunt on every double-handed backhand I hit. I literally had no idea and now I'm totally aware of it! (I don't if I'm doing any forehand or if I have to do a stretch one-handed backhand…!)