Memtest 86 is for RAM testing if you want to run it.
For data integrity-
On some of the Rescue DVD downloads there are all kinds of tools you can use to dx problems.
I know you already used smartctl -t but there are more commands on this page.
Recently the dmesg command showed me bus error after bus error and an interface fatal error.
In addition to that a bad CRC Cycliccal Redundancy Check too.
I found out that my HDD is failing.
If there is an application to test the front bus between the processor and the drive I have not found it yet but I'm trying.
This article might give you knowledge to help your issue.
What you need is a Diagnostic Tool with Advanced Dianostic Capabilities--
Sorry I could only find the ones I think for a computer.
The ones I came across were for a car.
But like I said I tried-
Hope this helps as I gave it my best go-