Oil problem?

My jeep 1998 cherokee classic was running fine, went to have oil changed, synthetic 5w 30 was put in, after about 200 miles bearings started making noise, went back had oil changed to 10w 40 reg oil, car runs at 210 deg, as always had, but still bearing noise, oil pressure at idle is 25-30, at 2000-2500rpm 40+psi, dont know why this noise would just suddenly start, car has 122000 mi orig, org owner always had oil changed at 2000 mi intervals. So what gives? Did oil pump go/ sending unit? And if it is pump how hard is it to change? And do you think it damaged bearings? Car sounds like a diesel at times. It has the 4.0 six engine and is a 4x4.