has anyone had this problem? can you describe the effects?

 

Engine runs OK at low speed and throttle, but has no top end and poor response. May sound odd at full throttle. Pull the bolts at the downpipe to converter flange and look at the front of the converter. The "grid" should be all open holes with none plugged and no melting. It's also possible to measure using a pressure guage if there is a fitting to attach to the exhaust manifold. Sometimes the catalyst in the converter will break apart in which case it may rattle.

They can clog if the engine is run too rich. They melt when overheated. Breaking apart seems to be a combo of bad luck and maybe poor design/manufacture.