Whistle Sound From Engine On My Yaris

[negativepitch]

I have a 57 plate yaris 1.3 SR,

in the last two days I have noticed a whistling sound coming from the engine when I start up and also when driving which I have never noticed before, it increases with the revs, I did push the car the other day in third, not taking it into the red but not far off going up a hill, Im not sure if this may have caused it, no engine lights are on and it drives fine, apart from this faint whistle, its not loud, it sounds a bit like wind noise whistle, but its not wind noise.

does anyone have any ideas, or does their yaris have a whistle sound on the engine as is it normal, it also sounds like a turbo whistle, but the car doesnt have one as far as I know

I have only had the car about 7 months and it only had 17000 miles on the clock as it was a second car for a lady, I bought it from Toyota Bridgend, so I know the car is a goodun. its like new inside and out and the engine bay is almost spotless with a full toyota service history

many thanks for any replies