Hissing noise under acceleration - driving me mad!

[kerm111t]

Hi all

Wonder if anyone can help shed some light on a hissing noise I'm getting from the rear of the car under acceleration? The car in question is a 2002 Elise 111S.

First noticed the when reversing the car a few weeks ago but is now noticeable in first, second & third gears (probably does it in fourth & fifth but I wouldn't be able to hear it). Only happens when I apply the throttle (usually when I've just changed gear) and only for a few seconds at a time. It doesn't make any noise at idle or when revved in neutral, only when in gear (ie. when driving). If I dip the clutch the noise completely disappears.

A 'hiss' is probably the closest description I can give - sounds like someone's shaken a bottle of coke and is holding their thumb over the top, just letting out a little bit of air for a few seconds every time I apply the throttle. The noise seems to be much more noticeable when the engine is cold, though it isn't completely disappearing when warmed up. There's also no loss of power and no fluids are leaking - the car runs perfectly well, its just really irritating!

Wondered if it could be a vacuum leak, but then I'd assume the noise would be present at idle? Also wondered if it could be a noisy belt? 

In conjunction with the hissing noise I occasionally also get a rattle which may or may not be associated. Notice it over bumpy roads, but also when accelerating too (usually its either rattling or hissing at me - feels like there's a rattlesnake in the boot!)  .

If anyone has had a similar issue, or has any ideas on what could be causing it that'd be much appreciated. Similarly, if you have any advice on how to eliminate certain causes, that'd be great. Might also try record and post a video of it if that helps.

 

Cheers

Rob

[kerm111t]

Hi all, this obviously didn't ring a bell with anyone but thought I'd post an update in case anyone comes up against a similar issue in future...

Managed to locate the source of the problem yesterday...

This hose had been rubbing against the side of the engine bay and had worn right through, creating a hole in it which was sucking in air. Must have been doing it for a long time (I've only had the car a few months) but only recently got to the point where it was noticable.

Due to where it was located it was essentially sucking itself to the side of the engine bay at idle (so wasn't making a noise) but under load it was obviously drawing in air through the hole and making the hissing sound.

A bit of tape over the hole has removed the noise completely, so now just need to replace the hose! Relieved it wasn't anything mechanical - now just need to locate the source of the rattle which is still present (must have been unrelated).

I guess it just wouldn't be Lotus-ownership if there wasn't some noise or another to diagnose...

[richbk]

Glad you got this fixed, and all under your own steam.

 

odd no one posted a suggestion, its usually a fountain of knowledge on here.

 

what colour is your car btw, looks a bit like my old BRG elise colour ??

 

richbk

[kerm111t]

Cheers Rich. Its called 'electric green' - only a handful cars were made in this colour apparently (I'm told it was a 'development' colour, though I haven't checked this with Lotus yet). 

CarThrottle made a video of the car (under previous ownership) which explains some of the history...