Does it sounds like a Soda can with rocks in it? My 1992 Prelude Si did that and It ended up being a Main bearing along the crank shaft spun out. It's still in the shop because it would cost to much to repair so I'm looking for either a cheap H22a or I will be Parting/Selling the whole thing. Personaly I would have it looked at before it gets worse. I got about $15,000 into my car and Its been sitting for about 6 months because of this.