Cannot speak as to the MBRP system, but:
I have a Flowmaster 942542 Series 40 Delta Flow, 2.50 Center In / 2.50 Offset Out muffler installed with NO CAT and still using OEM tailpipe from muffler to rear exit and get absolutely no drone at any speed. Never even hear it with windows rolled up and AC and / or radio on!
Replaced CAT and choke point with straight piece of exhaust tubing.
Total cost with labor by a local exhaust shop to install was around $150.00 ( I supplied the muffler from local parts store)
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount98 Dodge Cummins 24 Valve