Engine noises

Hi, My car was fine until i drove from manchester to london and back the other day, when i got home i could hear the engine rattling, it was like a tin of spanners! if i rev it, the noise goes away. then the next day i was driving to work and it started making a sort of loud whistle?? a bit like the noise a firework makes, just for a few seconds then it goes and it rattles again, then it will be completly fine???

Its driving fine, gave great fuel economy to london (for a 2.6 anyway), i have had quick look around the engine but there is not really much to see! im stuck in work till thursday and its dark when i finish so cant really see anything obvious.

Its booked in for a couple of new tyres on friday and i have asked them to change the oil at the same time, i know the last owner changed the oil himself and was wondering if maybe put the wrong oil in ( had been full audi service history till then), but i have had it 6 months and the engine has been perfect.

Has anybody had anything like this or got any ideas?

Cheers,

Ste.

Thanks mate, i will check the tensioner, i really hope its not that though!!!

Ste.

£6k for a new engine!!! the car cost half that!! it would be new car time.

Im using it as little as possible but still need to get to work, just keeping fingers crossed!

this morning i was sat in traffic and it started rattling really bad, it had not done it the day before, and i noticed that when i put the clutch down it slowly died away, so im thinking maybe clutch release bearing?? it feels down on power but then im driving it like a kitten! Also noticed that the power steering fluid was low, i only topped this up about a month ago?

Its in for an oil change in the morning and im going to ask them to have a look at the same time.