Metallic whine/rattle on deceleration

[Mikuma]

Just bought a 2ZZ swapped MR2 which was done by Rogue back in March. But it has an annoying metallic whine/rattle from the rear of the car when I take my foot off the gas, which is quite loud to be fair. But when accelerating it disappears. It's louder when taking off gas at higher speeds.

It disappears completely once the car has been driven for around 45 minutes and everything is at temperature.

It has a lightweight flywheel and competition clutch fitted.

I've thought it might be the exhaust shield touching the backbox (Rogue job), but not sure why it disappears when it's all hot? The backbox does look close to the shield to be fair.

Any suggestions on what this might be? Appreciate description is a little vague, not particularly mechanically minded! Oil looks fine and is at full.

I'm giving it a fresh oil change next weekend (including gearbox)

Cheers!

[Dev]

 It could be the gear box fluid.  If it's not properly filled or if you are using GL5 fluid it can whine on deceleration.

[StuC]

Just bought a 2ZZ swapped MR2 which was done by Rogue back in March. But it has an annoying metallic whine/rattle from the rear of the car when I take my foot off the gas, which is quite loud to be fair. But when accelerating it disappears. It's louder when taking off gas at higher speeds.

It disappears completely once the car has been driven for around 45 minutes and everything is at temperature.

It has a lightweight flywheel and competition clutch fitted.

I've thought it might be the exhaust shield touching the backbox (Rogue job), but not sure why it disappears when it's all hot? The backbox does look close to the shield to be fair.

Any suggestions on what this might be? Appreciate description is a little vague, not particularly mechanically minded! Oil looks fine and is at full.

I'm giving it a fresh oil change next weekend (including gearbox)

Cheers!

Why not get Rogue to diagnose it?

[shnazzle]

I think all 3 of our 2s have done this. One more than the other two. 
As Dev says, it's likely the fluid.
But if you're stopping by Rogue, might as well get them to double check