M38a1 clattering noise ? Drivetrain

[JayO]

Hi everyone. I am driving a new to me 1970 M38a1 drive train.
I just completed a restoration. I did not look at the clutch
Vehicle starts and drives well
Transmission shifts very well
All universals replaced
All gearboxes gl4 gear oil 90w
Clutch adjustment 1 1/2 “ free play
In third at around 40 mph. There is a raspy rattling noise.
When I depress the clutch at 40 mph raspy rattling sound stops
It sounds like it is coming from gearshift forward / floorboards
Firewall centrally back
I reviewed my manual and clutch springs are mentioned
This is not my expertise at all
Any thoughts?
How should I approach this?
Thank you for helping me
Jay Orchard. London Ontario
1970 M38a1. CND 3

[wesk]

Remove the entire center floor cover. Get a stethoscope and have someone drive while you listen and try to pinpoint the source.