The engine on my 95' 530iA was rebuilt about 15K miles ago (previous owner). I've had the car for about three months now, and it can have a seriously rough idle at times. Sometimes it's very smooth... sometimes it's very rough. About half an hour ago, I started up the car and it kind of gurgled in an alarming fashion. When I put it in gear, it was fine. At a series of stops, it idled in its normal, mildly rough way. When I got to work, I left it on and popped the hood to listen to it. It sounded... okay. Keep in mind that I am not a "car guy", so it could sound like Death itself and I wouldn't know the difference. The only weird thing I heard was a high-pitched (but not screechy high) little hum that regularly dipped and rose back to its normal pitch while the car idled. I'll probably take it in next week for a tune up, but it seemed kind of strange to me. Any ideas? Thanks.