Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.
I think it will be important for me to possibly listen to this rattling sound if you could possibly record it and upload it for me to review.
We need to find if it is internal or external and or related.
If there is an internal noise like that it may have an mechanical internal failure. Past that would require some basic up front testing in order to try and find the problem which includes if gas checking spark and ignoring if diesel, then checking fuel pressure, battery via professional load tester, compression, codes, etc.
Otherwise without a point of reference to start it will be hard to proceed as you will need a more narrow area to focus on the problem vs it being just about anything at this point.
Please rate my answer when ready. Bonuses are appreciated.
If for any reason you are not satisfied please reply back to me for further assistance to which I will be glad to help you. If you have any problems for any reason please reply back and let me know.
Thanks again for using justanswer and have a great day!
If you need any further assistance you can reply back at any time for my help.
I'd be happy to answer any other questions you have even if not related.