Boy oh boy, I can't stand rattles and squeaks. In our 2007 E350 PC-2350 (no slide out) we had an orchestra of them when the rig was new. One by one I chased them down with great success, but it is a process that never seems to rest. I have to say that considering what we are driving, I managed to quiet-down our trips comfortably so.
Here is a list of things I have done.
- Have the right tire pressure, not over-killing on PSI.
- Inspect the entry door frame perimeter screws making sure every one is tight to the main house. I was surprised some were sheared off, especially the two on the bottom through the threshold.
- Spray a "touch" of silicone lube in each cabinet door spring latch. Try one latch and wait making sure the plastic does not melt. Some seemingly harmless sprays literally melt the plastic latch.
- Install rubber drawer liners everywhere, even in utensil trays.
- Place paper towels in between stacked cookware.
- Use Corelle plates because they stack very tightly and take up very little space.
- Contain all non-perishable food that is in cans, bottles and similar, in small baskets, then placed in cabinets.
- Chronic microwave oven squeaks solved through spiked "T" nuts, machine screws, and felt pads
- Flip-up counter extension, added felt pads in critical places on hinges
- Placed a thick silicone pot holder on the stove grates, then set the covers on.
- Opened up the TV and placed many felt pads throughout to prevent the metal shielding from singing
- Roof top crank-up antenna, added felt pads on the bottom feet and wing tips.
- B+ front cap cabinetry, added screws per Phoenix, Kermit's instruction.
- E350 chassis, replaced front coil springs with lower-rated ones that better match our "actual working" load, softening the ride up front. The softer the suspension, the more quiet the ride.
We have thermal windows which I think also helps with general road noise. We do not have a slide out in our PC so I wouldn't know if they are a source of noise. It would be interesting to read from others concerning their slide out(s).
When felt pads were called for, I use this type sold everywhere, but just $1 at Dollar Tree.

When I solved the bigger noise generators, the lesser ones rose to the occasion. Eventually I reduced noise to wind, tire, and general machine-rumble noises that cannot be addressed without stopping motion altogether.