Check if the HDD have self monitoring activated. Self monitoring is called S.M.A.R.T. if disabled try to activate it from your pc bios if not possible use a proper tool for your HDD.
Try a PC side HDD scanning/repairing tool to see if your HDD has bad sectors and try to repair them with these tools. I believe that communication between PS2 and HDD is not the same as in PC and HDD.
So try to fix the problems of the HDD on PC and if nothing odd/strange is found try again in PS2.
Also try to use HDD with another network adaptor to see if the problem may be caused by the adaptor.
If the problems remain you should think about changing the HDD completely to prevent loosing data because sooner or later that HDD will give more problems and then fail completely for safe data holding.
PS2 SCPH-70004 V12 PAL + HDCOMBO + 160 GB Samsung HDD + OPL 0.9.1
PS2 SCPH-70004a V13 PAL Satin Silver
2 x Official Sony 8mb card +FMCB 1.8c + uLE 4.42b
Datel Max Memory 32mb card +FMCB 1.8b + uLE 4.42
Memor32 + Memento FW 1.2e