screen flickering

I have strange screen flickering problem ( macbook pro 13" retina late 2013 Yosemite . Screen flickers while i am working and not moving mouse or touchpad ( not with key board movement) !

If I leave it for sometime as the screen saver pops up the flickering stops. Some times system shuts down and starts up showing 'sleep wake error'

Took the system to service centre they even reinstalled OS, opened the back and reconnected components after cleaning the contacts and I still have the problem. The frequency of occurrence was less initially but now its very high.

I am again taking it to service but I think they are clueless.

Please help,

Thanks

Niranjan

Model Name: MacBook Pro

Model Identifier: MacBookPro11,1

Processor Name: Intel Core i7

Processor Speed: 2.8 GHz

Number of Processors: 1

Total Number of Cores: 2

L2 Cache (per Core): 256 KB

L3 Cache: 4 MB

Memory: 16 GB

Boot ROM Version: MBP111.0138.B15

SMC Version (system): 2.16f68

Serial Number (system): C02LW14UFH04

Hardware UUID: E5F42145-1AF5-5D62-BB73-751914674390