Wheel dependent noise

[graham.reeds]

Since I have been running in near silence (ie no radio) I have been learning the noises of my car but there appears to be a sound that is dependent on wheel speed and seems to be coming from over my left shoulder.  It sound like something rubbing and the closest I can imagine is when I am working on the axle of my gokart and I can hear the brake blocks gently rub the disc.

 

I can say that it is wheel dependent because the frequency of the noise rises and falls with the wheel speed and doesn't depend on gear (I put it in neutral on a downhill section to test this).

 

The best I can think is the rear left brake disc.

 

Can anyone who knows Caymans better suggest alternatives and how to check these hypotheses?

[Beanoir™]

Could be pads if they are running low?  When were they last changed? 

 

Would also check tyres, again how old and what brand are they?  I've twice had old/worn/misshaped tyres cause a similar noise (MX-5 and a Boxster)

 

Wheel bearings is not a common issue, but always possible. 

[graham.reeds]

The Cayman, despite the age has only done a little shy of 24k miles.

 

I don't know if or when the tyres and brakes were changed.

 

It has been in to Resolution Porsche for a car spa and the while a lot was corrected (rear bushes, hoses) the brakes weren't one of them. By my own test of feeling the lip I am guessing they are about 50% done and the tyre tread depth is similar.  I was planning on changing the tyres when I get 30k on the clock and brakes possibly 35k(ish).