Its prolly a bearing within the transmission of some sort. Theres about 4 bearings inside the transmission (im not familiar with 240 trannies) but its prolly not possible to tell unless you crack open the transmission casing, and check for sure. The throw-out bearing is in use when your clutch is engaged, so if you hear the grinding sound when you disengage yourclutch like you said, then it is not a release bearing. Your going to have to either open the transmission casing yourself and check to see which bearing it is (if you are familiar withtransmissions) or take it to a transmission dealer if you are not familiar with transmissions. The reason I know all this is because last month my 1990 Integra was doing the exactsame thing as your car. I thought it was the throw-out bearing aswell, but turns out it was one of the bearings within the transmission. Long story short, Mister Transmission wanted $400 bux for the labor and parts to fix my transmission. I decided against that idea, (since my transmission was in pretty rough shape, and could use a rebuild, or a completely new transmission), and I opt to buy a new transmission for my car. Total cost: $500 fortranny, and $150 for install, all covered by 90 day warranty
Keep in mind these are Canadian prices. Hope this helps you with your problem, and good luck!
