Just for test purpose, I've just tried the following:- please be aware that what I did is NOT allowed, as I took the liberty to change the sound.cfg file which is property of PMDG -I deleted the three touch_down entries, which means no touch-down sounds played at all: doing this got me rid of the stutters. No more stutter at touch down.I have restored the original PMDG sound .cfg file afterward, but I just wanted to make sure and let you know.

I'm sure I read somewhere that the puff of smoke and the tyre squeal on touchdown puts a high load on the graphics card that it causes the stutter.