Something is in the pipeline… dry conditions increase the creaking issues on a lot of full suss bikes… not just Marin 😉
I use a pure silicon spray like I do on my fork dust seals… that's worked and like a lot of bikes sometimes the creaking goes when it rains as well.
DO NOT use tf2, gt85 or the devils piss which is wd40 😀
It's not just you, the frame works great…But they are looking into it..
I empathise with you… 🙁
A couple of things you can try… change the rear qr for a shimano…rather than the hope, that's fixed it before.
check the bolts on both rear drop outs. Also we have had creaking from the hope rear freehubs, and also the chainring bolts coming loose.
But at the end of it some self lubricating pivot washers or brass ones even could sort it.
Have a word with your dealer or Grant at atb sales… 8)
I have a frame that creaked after only a 100 miles back with the whyte R+D department for them to asses… with my opinions attached 😆 No feed back yet though…think it should be a reasonable hassle free fix…
here's hoping!