Lattitude 5420/30/40 sound stuttering

HI, work at a factory and there is a few laptops (from 5420, 30 and 40's models) that have the same issue.

the steps that i already did : 

tested 9 sound driver from dell website - still stuttering
test 2 realtek sound drivers - still stuttering
tested 4 video drivers (intel and dell) - still stuttering
tested network drivers from intel and dell - still stuttering
tested on network cord - still stuttering
tested on wifi - still stuttering

tested using usb headset - WORKED


Dell support replaced Speaker - still stuttering

Dell support replaced Motherboard 3x (yes, 3 times already) - still stuttering

Test windows using Hiren´s usb windows PE - WORKED

replaced dow windows installation with same drivers from hiren´s usb windows
same sound driver - still stuttering
same network driver - still stuttering
same video - still stuttering

test achp/raid - still suttering

check HDR options (settings>display>HDR>battery options>optimize for quality) - still stuttering