Hello all! I have a 2003 SL55 AMG with 70K miles. It sat for a long time and I recently replaced the batteries. The car now makes 3 notable sounds of concern.

1: Loud hissing sound from under driver's seat. The hissing is present anytime the seat is moved, and then slowly fades away. Possibly PSE? It is most certainly directly under the seat, near the left side. Does not matter if car is on or not.

2: Rapid and loud ticking from passenger side trunk support. The very base of the trunk support which binds it to the car makes a very loud and rapid ticking noise, which is consistent and continuous for about a minute with the car off. Does not matter if car is on or not.

3: This one is the strangest... loud deep thumping sound at regular intervals from behind the cabin, but in front of the trunk area. Consistently thumps twice, one "on" and then "off", accompanied by slight electronic sounds. Only present with key in ignition off. Strong enough to vibrate the car, this one I am most confused about.

If anyone has any ideas on what the issues could be, I would love to hear them. Ask any questions and I'll make sure to answer them.