What was found
WHAT APPEARS TO BE FALSE RETURNS APPEAR APPROX 2 O'CLOCK POSITION BETWEEN 160NM-40NM (RIGHT SIDE OF DISPLAY) AND THEY CONTINUE TO SELF GENERATE IN THE ABSENCE OF ANY SIGNIFICANT WEATHER WHILE AT CRUISE. GROUNDED - YES. INSTALLED NEW WEATHER RADAR R/T. NO HELP. REINSTALLED ORIGINAL R/T REF B737-800 AMM 34-43-41. FOUND INNER LINING OF WAVEGUIDE ASSEMBLY PEELING. REPLACED ENTIRE WAVEGUIDE FROM R/T TO ANTENNA DRIVE UNIT REF AMM 34-43-21-400-801. STILL STRONG RETURN AT 2 O'CLOCK. REPLACED ANTENNA DRIVE UNIT WITH ORIGINAL FLAT PLATE REF AMM 34-43-11-000-802 AND REPOSITIONED AIRCRAFT FROM HGR-4 TO HGR-3. OPS NORMAL, NO RETURN AT 2 O'CLOCK. ACCOMPLISHED WXR SYSTEM OPERATIONAL TEST REF AMM 34-43-00-710-802-001. OPS NORMAL.