My 1999T GS300 SE has an annoying high pitched rattle / buzz which comes in intermittently at higher points on the rev range when under load. The technician at Lexus Leicester has tried to solve it over the past few services, even having had the car for a number of days but to no avail. The problem has no impact on the car's performance. I wonder if anyone else has had similiar experiences or might know what this is? I thought it might be a loose fixture under the car that oscillates when the engine revs get to a certain frequency...all advice much appreciated. Marcus.

maybe an exhaust heatshield

Welcome to the club

try the manifold shield... both under the bonnet and underneath the car... this is what usually tends to become loose after a while.

I took my underneath ones out because they were a pain and kep coming loose

Thanks all for your advice. It's going in for a B service next week and they promise to finally fix it. I'll be sure to pass tthe advice on, I just hope they believe me!