Ihave a strange noise that sound somewhat like an exhaust leak however I was unable to locate any exhaust leaks. It is a ths, ths sound and or rattling sound that appears to be coming from the rear of the engine that is heard when the Mini is under power (foot on gaspedal). Sometimes the sound fads,increases in intensity or disappears abruptly but then later sneaks back. The noise somewhat disappears in lower gears, 1st, 2nd and 3rd especially when the Mini is not under power (foot off gas pedal). I believe it is in the exhaust system because the noise is more prevalent when the Mini is under power and motoring. Note: Stock exhaust system, only change was different chrome exhaust tip several years ago. Oil pressure is 50 plus pounds and the oil level is approximately ¼ quart low. The Mini has 86,000 miles, original clutch, all original belts and chains, etc. Only items changed are the filters and oil at 5,000 (Synthetic Mobil 1). The noise is not present when the Mini is stopped, however one time I thought I heard the rattling noise when I stopped in my garage. Any Ideas what this is or how it fix it?