I think I found the RPM range that the hemi does not like. At highway speeds 68-72 There is a humming noise, you can also feel it in the pedal. RPM 2100-2200. What you do is get it up to that speed or rpm range slightly lift off pedal then come back into it. You will notice a slight vibration and noise. This has been reported in other threads. You guys think it is bad for the engine if you leave it in this range?

 

I seem to get this in my AWD RT at 74-76 mph only... possibly driveshaft is off balance by like 10 mcg.

 

My guess is that you are experiencing MDS mode. On my RT I have the Magnaflow exhaust and I can tell exactly when MDS kicks in and out. When MDS kicks in there is a drone from the exhaust and a slight vibration that can be felt with a light touch on the steering wheel and the shift. Love that MDS [&o]

 

Same thing on mine with Borla exhaust!

 

But it does sound like it is coming from the rear. Does'nt the MDS kick in at other RPM's also so would'nt you hear the same noise. Most highways are 55 mph so the MDS would be useless

 

MDS does kick in at other RPM's. The resonances are just stronger at some RPM's that others. Between 1500 and 1800 The harmonics from the exhaust do sound like they come from the rear. The way you can tell if it is MDS is to step down on the gas a little when it starts. Once the CPU senses more torque demand that is available in MDS mode it will immediately go back to 8 cylinders and the noise you are hearing should go away.

 

I noticed the same with my RT. I considered it to be the drone when MDS kicks in at this RPM range.

MikeyB

 

If this is true than putting 5w30 in a hemi does not diable the mds system like most owners think.

 

Why the crying face? You want to waste gas while idling down the highway?

 

I'm running 10w30 Mobil 1 synthetic. MDS works fine

Yeah, That's what I keep telling myself. I do like the savings. I hate the drone though. I'm convinced that is the reason for the huge stock resonators. It seems to me that DC could have given us a good Mass Air Flow system with a more free flowing exhaist that would get the mileage without the MDS.

I may not love everything about it but I still love the car.