I am opening a new thread as the first one was locked.
First of all, I'm sorry not to have seen this earlier. I've been very immersed in developing another aircraft for the new MSFS and don't check the forum here regularly as the product has been released for a long time now.
Concerning the startup sounds. The sound was done by Turbine Sound Studios. My understanding is that many sounds were recorded from an DC-8, but I don't know about the startup sounds specifically. It's an old aircraft and there are going to be issues in getting every sound as authentic as possible. That said, I think this is the first complaint about sound I have heard and I know there are several ex-DC-8 pilots and engineers that have purchased the product.
As for the vibrating scenery and difficulty while hand flying during climb out, it's difficult to know how to help as I have never experienced this behaviour. I think maybe two users have reported a similar issue but as I recall, I was never able to identify a cause.
The first thing to check is whether XML Tools is properly installed. In your main FSX directory there should be an FSXTools.dll file. If it isn't installed properly, many systems, including stabilizer trim, won't work properly. Do the trim handles move when you adjust the trim? Do the spoilerons move when the aircraft is on the ground? If so, then XMLTools is installed and working as it should.
Also, are you using FSUIPC for your control inputs? I recall that this caused trouble for some users in the past.