I have the Mach solo, center exhaust, on my coupe. I do not have a hfc. I hear no drone in my car. I haven't had the hard top on in three years and don't expect to ever install it again. The soft top has been off all summer but will put soft top on when we head to mkc West Virginia week long event, next month. Love my solo Mach exhausts that I have on both my Solstices.
07 Aggressive NA, 11-06 SOLD 9-17-08
09 WickedGXP9-25-08 Auto, Red calps,shorty antenna,windscreen,dibit & bkup light covers, leather armrests/console & door pockets,de-badged, pulsing 3rd light,GMPP CAI&tune, DDM susp set,Clear bra,garage opener in header, JPM lumbar,SOLO Mach Shty cat bk
09 Aggressive GXP Coupe 4-16-14, #577, Auto,soft top,Red calps,GM tune,GM acc whls,Conti Xtreme contact tires,pulsing 3rd light,red eng cover, DDM susp set,SOLO center Exh, Norm Valance