My 89 745T has aquired a rather annoying deep exhaust vibration under acceleration between 2000-2500 rpm, peaking about 2200. When I installed a low mileage 93 B230FT last April I put in new engine mounts (liquid filled)I got from RPR. I am unsure as to their manufacurer. Last week I put a new trans mount in, but I felt no difference. The car runs excellent otherwise, getting consistently better mieage than I did with the previous motor. Driveshaft center mount bushing was changed last year. All rubber exhaust mount are not that old, and a broken downpipe bracket to bellhousing bracket was replaced with the engine swap. First muffler has been eliminated, and turbo is an upgraded unit from Cherry Turbos. I am thinking of either 1) buying the optional Volvo exhaust bracket that mounts to the trans mount (or fabbing my own as I've read in the archives they are that robust, or 2) having a flex section welded inline on the downpipe before the cat flange. A lot of other 4 cylinder turbo and many non-turbo cars have one welded into their downpipe from the factory for the purpose of absorbing movement and vibration. Most aftermarket downpipe also have flex sections. In addition to the 2 ideas, I could replace the engine mounts with OEM Volvo ones.
Which one should I do? Which would make the biggest difference? Thanks for any words of wisdom, and all the advice I've ever gotten here.