[ QUOTE ]
I only noticed a difference when using them in piston twins
[/ QUOTE ]
I have a pair of 20XL's, and I get a buzzing noise sometimes (particularly on climb-out) from the ANR and it only happens in the twin. I sent them in and Lightspeed replaced a bunch of stuff, but it still does it.
BTW, Lightspeed was very good with their customer service. My set is waaaay out of warranty and they serviced it, including new ear seals and other parts, for free.