New owner of 2013 SL63 AMG with ABC ...only has 14K miles. Runs great but I noticed a very faint shudder/low frequency vibration every 30 seconds...its on for 2-3 seconds...then off for 30 seconds...then on again? It seems independent of whether I have sport suspension on, or either comfort or sport activated. It is very faint and I only notice it when travelling low speed 20-30 MPH with top up and radio off? Is this normal for ABC system to pulsate or does it indicate a possible issue with ABC pump, dampers etc? Thanks for your input.