Thanks for the comments.
Checked the fluid and that was all fine, a tad on the low side but nothing to worry about.
I took her in my local Lexus dealer yesterday for a free checkover. Turns out that my rear pads are 85% worn - no biggie there. But apparently my parking brake cables are binding which is causing the noise. There are 2 of these that now need replacing aling with the pads. Obviously Lexus are looking for an extorntianate amount (£500+) to supply and fit these, therefore I am going to source the parts myself and get them fitted by my local garage and I should save near on £300!
I can get brake pads no problem. I am having problems finding the brake cables though. They are part numbers:
46420-48170
46430-48170
Been trawling all over the net for hours and can only find these from a US Website that only delivers into the US.
Anybody know where these can be sourced in the UK without going to a Lexus dealer?
Cheers