SoSuperior

try to install the lastest drivers they have that are not beta so download a stable build of the driver and if that doesnt help then i woul suggest you to reinstall windows all over again and make sure you back up your data

the i7-4900mq is a great choice and that since you are also upgrading the ram you should get a good mhz rating from the ram so try to get something higher

I have the lenovo y510p also and i have notice that many people are getting NGFF MyDigitalSSD which i would recommend because it has great performance and that you should install an OS onto it also, and for the 2.5 sata drive you should try to get an ssd like for an example a Samsung 840 pro which is a good ssd and if you are going for a hhd then you should consider a 7500 rpm or higher rpm drive like a wester digital caviar black 7500 rpm and if u get either one of them that you should consider installing an OS onto the NGFF MyDigitalSSD and use the 2.5 drive as storage.

have you tried to re download all sound drivers and reinstall all of them from the drivers partition?