Hi alex,
We had the exact same issue in our network, caused by “ghost rach”.
The RACH counters can really confirm the existence of ghost RACH. You have to gather all those counters (from CPI), there is a dozen of them.
No need to do a trace, you ‘ll waste your time.
Ask for the Market Adaptation that will automatically reject suspected ghost rach. Ericsson has developped such M.A. and we are using them on my network since 5 yrs !
Tuning the Timing Advance is, I think, the simplest way to do it though.
But, there, here you have you answer : your issue is caused by Ghost Rach.
further confirmation : look at nightly values. Ghost RACH should be also seen during the night.
If you see spikes, and only on specific cells, then you may want to scan the area with a scanner, and find what kind of equipement is polluting your freq band.
If you see a background noise, all along the day, then … nothing you can do. EM pollution 🙂
br / pix