I am from N.E.England (Durham). My dialect is termed "Pitmatic", which is now slowly dying out. It is neither Geordie (Newcastle) nor Mackem (Sunderland). It is a Durham/Northumberland rural dialect with 19th century coal mining terms added, but its roots lie in northern Angle (with some Viking Norse).
I have searched the internet for a phonetic equivalent to the effect that I'm trying to describe, but have found nothing. However the general consensus (last night in the pub) is:-
at normal conversational speed the effect does not seem to exist, but if a "Y" word is stressed and/or pronounced slowly then an aspirated vibration can appear, or be made to appear.
Someone suggested - try to pronounce JORVIK very slowly as "ee-yor-vik". Don't jump from "ee" to "yor", but slowly slide, whilst maintaining the "vibration" of the "ee" & hopefully an aspiration should appear on or around the "y". If mastered, then the word can be pronounced without a long leading "ee", although its "vibration" is still required.
Hopefully this gives something like "{hyh}-orvik", with the hint of a 'soft g' in there somewhere. The important thing is the vibration. Someone else said that the "vibration" around the "y" was similar to that of the "s/z" of "leisure"/"azure" (but obviously without the actual "s/z" sound). I don't know if this will work, as I can already do it.
My apologies if this is diverging from the intent of this notice board, but I think it's important to remember that whilst the majority of OE literature is based on West Saxon, there are many non-WS dialects in England (and Lallans Scot).