Whilst sitting in traffic yesterday had my window down and noticed a sound coming from the engine every few seconds. Ok its a bit tough to describe like a tsst sound??? Like air being forced out for a second then it stops. I've noticed this happens when stationary and also on the move.

Is this right???

Did you have the air con on??

I've got my climate control set to auto so yes it may well have been on. Thats probably what it is then!!!!!

It is the A/C. You will also hear a sort of click from the front drivers side now and again.
Nothing to worry about .

But...if you want performance and power, turn the Air Con/Climate control off.

What differnce power wise does it make? I know that the a/c uses more juice!

the A/C make U loose 5 to 10 BHP I think!

The a/c will sap a little power as it is driven from the engine, hence the extra juice it uses too. Can't comment on my ST as I have only had it 3 weeks, but on my 206GTi the difference was noticable, like the difference you feel between a hot day and a cold crisp day, just feels more responsive and sharp. Another way is full of passangers and just you in it. I hope that helps, BHP wise no idea.

try switching it on whilst accelerating on a Mway and you will feel the power drop off!!!

I rarely use my A/C only when its hot or in the morning to heat up the car quickly. When the A/C on the car feel different and don't like it so it stay off most of the time

i hardly ever use it. in fact i think the only time it was on was when the mechanic took it for a run out - he left it on full! he also left my cd player on full too. how annoying

The air con should be used every once in a while because microbes can breed quiet happily in there. That's why you might see adverts for air conditioning cleaning. You can tell you've got funky air con if it stinks when you switch it on.

Yup, it should be used every so often. I try to keep its use to a minimum except when necessary, except to make sure it doesn't pack in - I'm pretty sure I read that the compressor can have problems if its left totally unused, as well as the probs that Pinky mentionned above. I think roughly half an hours use a month is more than enough to make sure its kept running smoothly.

And before anyone says "Ohhh but its winter I dont want cold air!"... in pre facelifts just change the temp and switch the air con on