Flickering guages

I plan to clean the grounds on my GT40 to see if it cures the following issues. Not major problems but a little annoying.

1 - Oil pressure guage flickers a little around otherwise appriopriate readings, esp on idle. The guage has always done this.

2 - Tach flickers around appropriate readings, also only round idle. This has only started a few weeks ago.

Could this be dodgy grounds or something else? All other guages are solid. All guages are less then 6 months old (Faria replacements). Engine was rebuilt last year.

Thanks,

Darren.