DURING CLIMB; AN MD-80 PILOT INFORMED BY FLT ATTENDANT THAT THE LEFT ENG HAD LOUD VIBRATIONS AND WAS NOISIER THAN NORMAL.

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DURING CLB; THE FLT ATTENDANTS CALLED TO SAY THAT THE L ENG HAD EXPERIENCED LOUD VIBRATIONS AND WAS NOISIER THAN NORMAL. BECAUSE THE ENG INSTS WERE NORMAL AND WX WAS VERY BAD AT ZZZ1 (SNOWSTORM) AND NOT MUCH BETTER AT ZZZ2; WHICH WAS OUR TKOF ALTERNATE; I ELECTED TO CONTINUE CLB TO FL230; LEVELED THERE AND WENT BACK TO THE CABIN TO LISTEN TO THE ENG. I COMMUTE AND OFTEN SIT NEAR THE ENGS SO I KNOW WHAT THEY SOUND LIKE. THE FLT ATTENDANTS SAID THAT THE HVY VIBRATION HAD CEASED. I AGREED THAT THE ENG WAS NOISIER THAN NORMAL; BUT IT WAS A SMOOTH SOUND. I CALLED THE FLT DECK AND INSTRUCTED THE FO TO OBTAIN CLRNC FOR FURTHER CLB SO THAT I COULD LISTEN TO THE ENG AT CLB PWR. IT GOT NO WORSE SO I ELECTED TO CONTINUE TO ZZZ3; WHERE MAINT MET THE ACFT. A VISUAL INSPECTION FROM THE AFT GALLEY DOOR REVEALED THAT SEVERAL COMPRESSOR BLADES WERE DAMAGED. BOTH ENGS' INTAKES HAD BEEN INSPECTED PRIOR TO GATE DEP SINCE WE HAD TO START AND TAXI TO THE DEICING AREA. FOR WHAT IT IS WORTH; BOTH ENGS WERE PLACARDED IN APCH IDLE SO WE HAD TO RUN THEM UP TO ABOVE 60% BEFORE TAXIING VERY FAR. THERE WAS SNOW ON THE RAMP AT THE LOCATION OF THE RUN-UP; BUT IT WAS SMOOTH SNOW; NOT CHUNKS OF CONTAMINATION. MY MAIN CONCERN WAS TO GET THE RUN-UP COMPLETED WITHOUT SLIDING. THE CONDITIONS WERE REALLY BAD TO BE OPERATING A PLANE WITH THAT PLACARD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED HAVING BOTH ENGINES PLACARDED IN 'APPROACH IDLE' WAS SOMEWHAT UNCOMMON. HE DOES NOT KNOW WHAT WAS THE REASON FOR THE PLACARDING. BUT THIS PLACARD REQUIRED THEM TO OPERATE THE ENGINES ABOVE 60 PERCENT. THE 'APPROACH IDLE' SYSTEM PROVIDES RAPID ENGINE ACCELERATION CAPABILITY FOR USE IN A 'GO AROUND' SITUATION. 'APPROACH IDLE' IS ALSO MAINTAINED AFTER NOSE GEAR TOUCHDOWN FOR 5-SECONDS TO PROVIDE RAPID ENGINE ACCELERATION CAPABILITY IN CASE OF A MISCALCULATED LANDING AND FOR REVERSER OPERATION. REPORTER ADDED THAT TRYING TO TAXI IN THE SNOW WITH THE HIGHER ENGINE IDLE MADE CONTROL OF THE ACFT DIFFICULT IN THE SNOWY CONDITIONS. THE HIGHER ENGINE IDLE OPERATION APPEARS TO HELP ASSIST IN A FASTER RESPONSE OF THE 'AUTOMATIC RESERVE THRUST SYSTEM (ARTS)' RESPONSE TO A PERCEIVED ENGINE FAILURE AND IS ALSO TIED IN WITH THE DIGITAL FLIGHT GUIDANCE COMPUTER (DFGC) AND ENGINE FUEL CONTROL.