A MD80 ENTERING HOLDING AT FL350 ENCOUNTERED A STALL BUFFET AT 241 KTS IN A 25 DEG BANK TURN. A THRUST INCREASE AND DECREASED ROLL RATE STOPPED THE BUFFET.

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AT CRUISE PRIOR TO INTXN ON ARR FOR ZZZ ATC ADVISED HOLDING AT NEXT INTXN; SPD OUR DISCRETION. WE TALKED OVER SPD; PDC STATED .69 MACH AT 120500 LBS; MINIMUM CRUISE SPD IN BOOK AT 120000 IS 229 IAS; HOLDING 2 ENGS IS 229 IAS ALSO. WE DECIDED .72 MACH WOULD BE OK. RIDE IS LIGHT TO MODERATE CHOP FOR LAST PORTION OF FLT SO THIS WOULD RESULT IN ABOUT A 245 KIAS. I SLOWED AND STABILIZED AT .72 MACH IN LIGHT CHOP; ANTI-ICE IS ON; AUTOPLT/AUTOTHROTTLES ARE ENGAGED AND NAV SELECTED. AT INTXN THE AUTOPLT ROLLS TO 25+ DEGS TO INTERCEPT OUTBOUND COURSE AS THE RIDE GOES TO MODERATE CHOP. A VIBRATION IS FELT IN AIRFRAME (FLT ATTENDANTS LATER RPT NOISE ALSO IN THE BACK). I GO TO HDG SELECT AND REDUCE ROLL ANGLE. VIBRATION GOES AWAY IMMEDIATELY. VIBRATION LAST 4-6 SECONDS WITH NO OTHER INDICATIONS. SPD DROPPED TO 241 IAS AND STOPPED. I ADVANCED THROTTLES MANUALLY (AUTOTHROTTLES WAS BEHIND AT THIS POINT) TO CLB EPR ON THE CHEVRONS AND SPD SLOWLY RETURNED TO OUR NOW SELECTED .75 MACH. AT .75 MACH AUTOTHROTTLES RESPONDED NORMALLY. I BELIEVE THE VIBRATION WAS CAUSED BY THE 25 DEG BANK WITH THE MODERATE RIDE AT ALT. THE AUTOTHROTTLES WERE SLOW TO REACT BUT THE SPD ONLY BLED OFF A FEW KTS. ACFT WAS EXAMINED AT ZZZ BY MECHS AND FOUND TO BE OK FOR SVC. I WILL ASSURE YOU I WILL NOT SLOW TO BOOK SPD IN THE FUTURE. WE DID NOT VACATE FL350. SUPPLEMENTAL INFO FROM ACN 776120: ON STAR INTO ZZZ ACFT APPARENTLY ENTERED INTO A VERY SHORT DURATION STALL. WITH ANTI-ICE ON AT FL350 ACFT WT OF 120500 LBS MACH .72 IAS OF 245 AND LIGHT CHOP THE AUTOPLT COMMANDED A 25 DEG BANK TO INTERCEPT THE OUTBOUND LEG FROM INTXN. AT 25 DEGS A LOUD RUMBLE WAS HEARD IN THE CABIN AND A VIBRATION WAS FELT IN THE COCKPIT.