honda knocking noise

hi guys I recently bought a honda integra 1.6 1998 the guy I bought it from told me it needed new drop links and a new exhaust bracket rubber towards the front, I can on ocasion feel a knocking under the gear box whilst driving over ruff road, also after driving it hard or reving it only sometimes there is like a knocking from under the bottom back of the engine its not a loud knock or hard and it fades after 40 seconds or so but just wondering what it is as the engine is ticking over perfect other than that and drives ok, I jacked it up the other day and the exhaust looked fine not hanging or anything. also it only heats up quater way when driving and half when idle but the fan does kick in at idle also if you drive it on a bit the engine temp goes down a good bit, just want some one to give me peace of mind as cant afford to go to the mechanic for the next couple of weeks cheers guys.