Lifter noise

I have recently developed a tapping noise on the right bank of my 1994 E 420 MB. They tell me it sounds like a lifter making the noise. The Auto has 126,000 miles on it. I change the oil and filter every 3000 miles, use Valvoline 10W-40 oil? Is there any way to get rid of the noise, aside from doing lifter job? Could the rocker arm have loosened up? I am looking for a quick fix to this problem if there is any. I love the auto but the noise is driving me crazy. My wife tells me it sounds like a marble in a tin can. Thanks for any help that I can get or suggestions that you may have for me. Ben